Magnetoresistive-effect thin film, magnetoresistive-effect element, and magnetoresistive-effect magnetic head

ABSTRACT

A spin-valve film used in a magnetoresistive-effect magnetic head includes an antiferromagnetic layer, a magnetization fixing layer, a non-magnetic layer, and a free layer. The magnetization fixing layer or the free layer is provided with a layered ferromagnetic structure which includes a pair of magnetic layers through the intermediary of a non-magnetic layer. In the layered ferromagnetic structure, a surface oxidation layer is formed on the surface of the non-magnetic intermediate layer to the side of the non-magnetic layer.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a magnetoresistive-effect thin filmusing the giant magneto-resistivity. The present invention also relatesto a magnetoresistive-effect element and a magnetoresistive-effectmagnetic head fabricated with the magnetoresistive-effect thin filmusing the giant magneto-resistivity.

2. Prior Art

Conventionally, there is a widely used magnetoresistive-effect magnetichead (hereafter referred to as the MR head) which uses magnetoresistanceof a magnetoresistive-effect element (hereafter referred to as the MRelement) to read signals recorded on a magnetic storage medium.

The MR element is a type of resistance element and varies electricalresistance according to an external magnetic field. The MR head readsmagnetic signals recorded on a magnetic storage medium by using the factthat the MR element's electrical resistance varies with a signalmagnetic field from the magnetic storage medium.

In recent years, there is an increasing need for a small, large-capacitymagnetic storage medium. For example, a technique such as narrowing arecording track width output.

From the viewpoint of increasing recording densities, the spin-valvefilm tends to thin the free layer for reducing its magnetic moment.However, thinning the free layer may degrade magnetoresistance.

To solve this, it is proposed to use a structure comprising a pair ofantiferromagnetically combined ferromagnetic layers for the pinned layeror the free layer by forming a non-magnetic layer between a pair offerromagnetic layers for the spin-valve film. This structure is calledthe layered ferrimagnetic structure (VS. Speriousu et.al; The 1996 IEEEINTERMAG,AA-04). The layered ferrimagnetic structure provides a 3-layerstructure by forming a non-magnetic layer between a pair offerromagnetic layers. Adjusting the non-magnetic layer thicknessantiferromagnetically binds a pair offerromagnetic layers. Theabove-mentioned non-magnetic layer is generally formed of Ru, Rh, Ir,Re, and the like.

When the pinned layer uses this layered ferrimagnetic structure, a pairof antiferromagnetically coupled ferromagnetic layers decreases anapparent magnetic moment for the pinned layer. Even if the free layer isthin, demagnetization applied to the free layer decreases. This makes itpossible to improve the free layer's sensitivity against an externalmagnetic field without excessively thinning the pinned layer.

Examples of the spin-valve film which uses the layered ferrimagneticstructure for the free layer are reported in studies by A. Veloso et al.(IEEE Trans. Magn. Vol. 35, No. 5, P2568-2570, September 1999) and thelike. Since a pair of ferromagnetic layers is antiferromagneticallycoupled in the free layer, an apparent magnetic moment for the freelayer can be decreased by maintaining the thickness of one magneticlayer associated with magnetoresistive-effect and adjusting thethickness of the other magnetic layer not associated therewith.Accordingly, it is possible to improve the free layer's sensitivityagainst an external magnetic field without excessively thinning the freelayer.

On the other hand, improvement of the magnetoresistive-effect changenecessitates consideration of increasing a probability that electronsscatter depending on spins in the spin-valve film and improving themagnetoresistive-effect change in the spin-valve film. Incidentally,this scattering of electrons is hereafter referred to as spin-dependentscattering.

When the layered ferrimagnetic structure is applied to the free layer,however, there is provided a new magnetic layer not associated withmagnetoresistive-effect. A shunt loss may occur in this magnetic layer.There is the problem that a resulting magnetoresistive-effect change isnot as high as expected despite the use of the layered ferrimagneticstructure for the free layer.

Japanese Patent Application Laid-Open Publication No. 11-8424 disclosesan example of the spin-valve film which increases the probability ofspin-dependent scattering as mentioned above. According to this example,a metal layer which easily causes mirror reflection is formed adjacentto the pinned layer and the free layer. However, many such metalmaterials provide low resistivity. Consequently, a current shunts to thelayer of such metal easily causing mirror reflection, raising thepossibility of decreasing MR head output.

Japanese Patent Application Laid-Open Publication No. 11-168250 and thestudy by W. F. Egelhoff et. al. (J. Appl. Phys. 82(12), 15 Dec. 1997)provide an example of the spin-valve film which increases theprobability of spin-dependent scattering as mentioned above. Accordingto this example, an antiferromagnetic film of oxide is formed in thespin-valve film. However, the antiferromagnetic film formed of oxidedoes not provide a sufficient exchange coupling force with aferromagnetic film used as the pinned layer. The antiferromagnetic filmformed of oxide lacks thermal stability and does not ensure thereliability as an antiferromagnetic film compared to anantiferromagnetic film formed of presently used ordered metal.

Further, the study by Y. Kamiguchi et. al. (The 1999 IEEE INTERMAG,DB-1) provides an example of the spin-valve film which increases theprobability of spin-dependent scattering as mentioned above. Accordingto the example, the spin-valve film contains a metal oxide layer formedin the middle of a pinned layer. However, forming a metal oxide layer inthe middle of the pinned layer thickens it. Thickening the pinned layerincreases demagnetization applied to the free layer.

Conventionally, the spin-valve film uses a non-magnetic layer with athickness of 2.4 to 3.2 nm formed between the pinned layer and the freelayer. From the viewpoint of improving the magnetoresistive-effectchange, it is desirable to make the non-magnetic layer as thin aspossible. However, thickening the non-magnetic layer excessivelyincreases an inter-layer coupling field between the pinned layer and thefree layer. A change in the free layer's magnetization direction mayalso change the pinned layer's magnetization direction.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in consideration of the foregoing.It is therefore an object of the present invention to provide amagnetoresistive-effect thin film which improves amagnetoresistive-effect change and provides high sensitivity against anexternal magnetic field by increasing the spin-dependent scatteringprobability of electrons. It is another object of the present inventionto provide a magnetoresistive-effect element which can efficientlydetect an external magnetic field. It is yet another object of thepresent invention to provide a magnetoresistive-effect magnetic headwhich provides high reproduction output and is suited for high-densityrecording.

A magnetoresistive-effect thin film according to the present inventioncomprises at least an antiferromagnetic layer, a magnetization fixinglayer, a non-magnetic layer, and a free layer formed successively,wherein: the magnetization fixing layer or the free layer is providedwith a layered ferrimagnetic structure which comprises a pair ofmagnetic layers through the intermediary of a non-magnetic intermediatelayer; and a surface oxidation layer is formed on the surface of thenon-magnetic intermediate layer to the side of the non-magnetic layer inthe layered ferrimagnetic structure.

In the thus configured magnetoresistive-effect thin film according tothe present invention, a surface oxidation layer is formed on thesurface of the non-magnetic intermediate layer constituting the layeredferrimagnetic structure. This increases the spin-dependent scatteringprobability of electrons, improves the magnetoresistive-effect change,and increases sensitivity against an external magnetic field. Thesurface oxidation layer's interface is extremely smooth. Consequently,it is possible to further thin the non-magnetic layer formed between themagnetization fixing layer and the free layer compared to the prior art.

A magnetoresistive-effect element according to the present inventioncomprises at least an antiferromagnetic layer, a magnetization fixinglayer, a non-magnetic layer, and a free layer formed successively,wherein: the magnetization fixing layer or the free layer is providedwith a layered ferrimagnetic structure which comprises a pair ofmagnetic layers through the intermediary of a non-magnetic intermediatelayer; and there is provided a magnetoresistive-effect thin film havinga surface oxidation layer formed on the surface of the non-magneticintermediate layer to the side of the non-magnetic layer in the layeredferrimagnetic structure.

The thus configured magnetoresistive-effect element according to thepresent invention is fabricated from the magnetoresistive-effect thinfilm with an improved magnetoresistive-effect change. This is because asurface oxidation layer is formed on the surface of the non-magneticintermediate layer constituting the layered ferrimagnetic structure.Accordingly, the magnetoresistive-effect element increases sensitivityagainst an external magnetic field.

A magnetoresistive-effect magnetic head according to the presentinvention has a magnetoresistive-effect element comprising a pair ofzonal magnetic shield members, a magnetoresistive-effect thin filmformed between the pair of magnetic shield members, a pair of biaslayers formed at bot ends of the magnetoresistive-effect thin film alonga longer direction, and a pair of thin-film lead electrodes each formedjust on the bias layer on a substrate, wherein: themagnetoresistive-effect thin film constituting themagnetoresistive-effect element comprises at least an antiferromagneticlayer, a magnetization fixing layer, anon-magnetic layer, and a freelayer successively formed; the magnetization fixing layer or the feelayer is provided with a layered ferrimagnetic structure which comprisesa pair of magnetic layers through the intermediary of a non-magneticintermediate layer; and a surface oxidation layer is formed on thesurface of the non-magnetic intermediate layer to the side of thenon-magnetic layer in the layered ferrimagnetic structure.

The thus configured magnetoresistive-effect magnetic head according tothe present invention is fabricated from the magnetoresistive-effectthin film with an improved magnetoresistive-effect change. This isbecause a surface oxidation layer is formed on the surface of thenon-magnetic intermediate layer constituting the layered ferrimagneticstructure. Accordingly, the magnetoresistive-effect magnetic headincreases sensitivity against an external magnetic field from a magneticstorage medium and improves output while reproducing recordedinformation.

As will be clearly understood from the above description, themagnetoresistive-effect thin film according to the present inventiongenerates a mirror reflection by electrons and easily causesspin-dependent scattering. This is because a surface oxidation layer isformed by oxidizing the surface of the non-magnetic intermediate layerconstituting the layered ferrimagnetic structure. Hence, themagnetoresistive-effect thin film improves a magnetoresistive-effectchange and provides good sensitivity against an external magnetic field.The surface oxidation layer's interface is extremely smooth.Consequently, it is possible to further thin the non-magnetic layerformed between the free layer and the magnetization fixing layercompared to the prior art. This can further improve themagnetoresistive-effect change.

The magnetoresistive-effect element according to the present inventionis fabricated from the above-mentioned magnetoresistive-effect thinfilm. Accordingly, it is possible to efficiently detect a slight changein the external magnetic field.

The magnetoresistive-effect magnetic head according to the presentinvention is formed of the above-mentioned magnetoresistive-effect thinfilm. Because of this, the head provides good sensitivity against amagnetic field from an information storage medium and produces a highoutput during information reproduction. Hence, the head is appropriatefor high-density recording.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional view of a bottom-type spin-valve film according toa first embodiment;

FIG. 2 is a characteristic chart showing relationship between a Cu layerthickness and an inter-layer coupling field intensity between a pinnedlayer and a free layer;

FIG. 3 is a sectional view of a top-type spin-valve film according to asecond embodiment;

FIG. 4 is a cross sectional and broken view of an MR head fabricated byusing a spin-valve film according to the present invention;

FIG. 5 shows a result of measuring a magnetoresistive-effect curve of aspin-valve film fabricated for a first example,

FIG. 6 shows a result of measuring a magnetoresistive-effect amount fora spin-valve film fabricated for a comparative example 1 withoutoxidizing an Ru layer;

FIG. 7 shows relationship between an Ru thickness and a coercive forcefor the entire thin film;

FIG. 8 shows a result of measuring a magnetoresistive-effect curve of aspin-valve film fabricated for a third example;

FIG. 9 shows a result of measuring a magnetoresistive-effect curve of aspin-valve film fabricated for a comparative example 2;

FIG. 10 shows a result of measuring a magnetoresistive-effect curve of aspin-valve film fabricated for a fourth example; and

FIG. 11 shows a result of measuring a magnetoresistive-effect curve of aspin-valve film fabricated for a comparative example 3.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in further detailwith reference to the accompanying drawings.

Drawings used for the following description may enlarge characteristicportions for easy understanding of these portions using clearlyrecognizable illustrations. Ratios of dimensions for each member maydiffer from actual values.

The following description exemplifies layer configurations, materials,and the like constituting a magnetoresistive-effect thin film. Thepresent invention is not limited to the exemplifiedmagnetoresistive-effect thin film. It may be preferable to choose properlayer configurations, materials, and the like according to intendedpurposes and performance.

The following describes a first embodiment of themagnetoresistive-effect thin film according to the present inventionwith reference to FIG. 1. A spin-valve film 1 is of a so-calledbottom-type and is characterized by a layered ferrimagnetic structurehaving a surface oxidation layer on a pinned layer.

The spin-valve film 1 comprises a base layer 3, an antiferromagneticlayer 4, a first ferromagnetic layer 5, a non-magnetic intermediatelayer 6, a surface oxidation layer 7, a second ferromagnetic layer 8, anon-magnetic layer 9, a free layer 10, and a protective layer 11 whichare layered successively on a substrate 2. It should be noted that thefirst ferromagnetic layer 5, the non-magnetic intermediate layer 6, thesurface oxidation layer 7, and the second ferromagnetic layer 8 composea pinned layer 12 having a layered ferrimagnetic structure.

The substrate 2 is formed of a nonmagnetic nonconductive material suchas glass and the like.

The base layer 3 is formed of a nonmagnetic nonconductive material suchas Ta. By having the base layer 3, the spin-valve film 1 improvescrystal orientation. In addition, the base layer 3 prevents thesubstrate 2's material from contaminating thin film layers constitutingthe spin-valve film 1.

The antiferromagnetic layer 4 is formed of a regular antiferromagneticmaterial and an irregular antiferromagnetic material using Mn such as aPt—Mn alloy, an Ni—Mn alloy, Pd—Pt—Mn alloy, and the like. It may bepreferable to form the antiferromagnetic layer 4 using NiO, α-Fe₂O₃, andthe like. Forming the antiferromagnetic layer 4 fixes magnetizationdirections for the first ferromagnetic layer 5 and the secondferromagnetic layer 8 constituting the pinned layer 12 as will bedescribed later.

The first ferromagnetic layer 5 and the second ferromagnetic layer 8 areformed of magnetic materials showing good soft magnetic characteristicssuch as an Ni—Fe alloy, Co, and an alloy containing one of Co, Ni, andFe. Together with the non-magnetic intermediate layer 6 and the surfaceoxidation layer 7 to be described later, the first ferromagnetic layer 5and the second ferromagnetic layer 8 form the pinned layer 12 having theso-called layered ferrimagnetic structure. The first ferromagnetic layer5 and the second ferromagnetic layer 8 are exchange-coupled to theantiferromagnetic layer 4 to fix the magnetization direction.

Providing the pinned layer 12 with the layered ferrimagnetic structuredecreases a magnetic moment on the pinned layer 12 and also decreasesdemagnetization applied to the free layer. The layered ferrimagneticstructure comprises a non-magnetic layer sandwiched between twoferromagnetic layers. By adjusting the non-magnetic layer thickness, thetwo ferromagnetic layers are coupled to each other so that eachmagnetization direction becomes antiparallel. It is possible to use Ru,Rh, Ir, Re, and the like for the non-magnetic layer formed in the middleof the above-mentioned layered ferrimagnetic structure.

The non-magnetic intermediate layer 6 and the surface oxidation layer 7function as non-magnetic layers formed in the middle of theabove-mentioned layered ferrimagnetic structure. The surface oxidationlayer 7 is formed by oxidizing the surface of the non-magneticintermediate layer 6. It is desirable to form the non-magneticintermediate layer 6 of Ru with the thickness of 0.4 to 1.2 nm.

The surface oxidation layer 7 is formed by oxidizing the surface of thenon-magnetic intermediate layer 6 and is made from an Ru oxide(hereafter referred to as Ru—O).

While the surface oxidation layer 7 is formed by oxidizing the surfaceof the non-magnetic intermediate layer 6, the thickness of the surfaceoxidation layer 7 generally should be 0.4 nin or less. The reason forthis is not always clear. However, it is considered that thenon-magnetic intermediate layer 6 is just oxidized to the depth of 0.4nm from the surface when the surface of the non-magnetic intermediatelayer 6 comprising Ru is oxidized as will be described in an embodiment2.

Since the surface oxidation layer 7 is formed by oxidizing the surfaceof the non-magnetic intermediate layer 6, the surface oxidation layer 7and the non-magnetic intermediate layer 6 almost maintain the sameinterface. The spin-valve film 1 is formed unbrokenly. Forming thesurface oxidation layer 7 containing Ru—O smoothes the interface. Thiscan cause the so-called mirror reflection which enables reflection andscattering of electrons by maintaining spin directions of electrons. Themirror reflection of electrons dramatically improves the probability ofelectron's spin-dependent scattering. Consequently, it is possible toimprove a magnetoresistive-effect change for the spin-valve film 1.

The surface oxidation layer 7 is formed in the pinned layer 12 havingthe layered ferrimagnetic structure. This makes it possible to thin thenon-magnetic layer 9 between the pinned layer 12 and the free layer 10compared to a spin-valve film which does not have the surface oxidationlayer 7. The definite reason is unknown. However, a possible reason issupposed as follows.

The following describes an experiment example for examining an effect offorming the surface oxidation layer 7.

We actually fabricated two spin-valve films. One is structured to havethe surface oxidation layer 7 comprising Ru—O in the pinned layer 12provided with the layered ferrimagnetic structure. The other has theconventional structure without the surface oxidation layer. Using thesespin-valve films, we measured intensities for an inter-layer couplingfield between the pinned layer and the free layer by changing thethickness of a Cu layer equivalent to the non-magnetic layer 9. FIG. 2shows measurement results.

The following shows the configuration of the spin-valve film having thesurface oxidation layer in the pinned layer provided with the layeredferrimagnetic structure. All values in parentheses indicate layerthicknesses in nm.

-   Substrate/Ta (5)/NiFe (2) PtMn (20)/CoFe (1.1)/Ru+Ru−O (0.8)/CoFe    (2.2)/Cu (t)/CoFe (2.5)/Cu (1) Ta (0.2)

The following is the configuration of the other spin-valve film whichuses no surface oxidation layer in the pinned layer provided with thelayered ferrimagnetic structure.

-   -   Substrate/Ta (5)/NiFe (2)/PtMn (20)/CoFe (1.1)/Ru (0.8)/CoFe        (2.2)/Cu (t)/CoFe (2.5)/Ta (5)

There is a slight difference between one spin-valve film having thesurface oxidation layer and the other not having the same in the pinnedlayer with the layered ferrimagnetic structure. However, such adifference is consider to be negligible for the comparison.

As shown in FIG. 2, the inter-layer coupling field intensity between thepinned layer and the free layer becomes minimum when the Cu layerthickness is in the range of approximately 2 to 2.4 nm for thespin-valve film having the surface oxidation layer. By contrast, for theconventional spin-valve film having no surface oxidation layer, theinter-layer coupling field intensity between the pinned layer and thefree layer remarkably increases when the Cu layer thickness becomessmaller than 3 nm. Consequently, with respect to the conventionalspin-valve film having no surface oxidation layer, setting the Cu layerthickness to as thin as approximately 2 nm will greatly increase theinter-layer coupling field intensity between the pinned layer and thefree layer. There is a possibility that a change in the magnetizationdirection of the free layer could also change the magnetizationdirection of the pinned layer.

Since the spin-valve film 1 provides the surface oxidation layer 7 inthe pinned layer 12 having the layered ferrimagnetic structure, it ispossible to thin the non-magnetic layer 9 between the pinned layer 12and the free layer 10 up to a thickness of approximately 2 nm.Accordingly, it is further possible to improve a magnetoresistive-effectchange for the spin-valve film 1.

Several methods are available for forming the surface oxidation layer 7by oxidizing the surface of the non-magnetic intermediate layer 6. Forexample, one method exposes the non-magnetic intermediate layer 6 to anoxygen atmosphere having a pressure lower than the atmospheric pressure.There is also provided the plasma oxidization method including ECR(electron cyclotron resonance) and the ICP (inductively coupled plasma).

The non-magnetic layer 9 is formed of a conductive non-magnetic materialsuch as, say, Cu, Cu—Ni alloy, or the like. Forming the non-magneticlayer 9 between the pinned layer 12 and the free layer 10 provides thegiant magneto-resistivity on the spin-valve film 1. As mentioned above,the non-magnetic layer 9 can be thinner than the non-magnetic layerbetween the pinned layer and the free layer on the conventionalspin-valve film. More specifically, it is desirable to set thenon-magnetic layer 9's thickness to approximately 2 nm.

The free layer 10 is formed of magnetic materials showing good softmagnetic characteristics as well as the first ferromagnetic layer 5 andthe second ferromagnetic layer 8. The free layer 10's magnetizationdirection varies with the external magnetic field. The free layer 10 maybe formed of a layered structure comprising an Ni—Fe alloy layer and aCo—Fe alloy layer. This structure makes it possible to improve thereproduction sensitivity of the spin-valve film 1.

The protective layer 11 is formed of a non-magnetic material such as Ta.Forming this protective layer 11 prevents resistivity on the spin-valvefilm 1 from increasing and protects the free layer 10 against softmagnetic instability.

In this spin-valve film 1, the pinned layer 12 is provided in contactwith the antiferromagnetic layer 4. Consequently, the pinned layer 12 ismagnetized in a given direction due to an exchange coupling forcegenerated between the pinned layer 12 and the antiferromagnetic layer 4.Since the non-magnetic layer 9 is formed between the free layer 10 andthe pinned layer 12, the free layer 10's magnetization direction easilyrotates in response to a slight external magnetic field.

When an external magnetic field is applied to the thus configuredspin-valve film 1, a magnetization direction of the free layer 10 isdetermined according to this external magnetic field's direction andintensity. The spin-valve film 1 provides the maximum electricalresistance when the magnetization direction of the free layer 10 differsfrom that of the second ferromagnetic layer 8 in the pinned layer 12 by180°. The spin-valve film 1 provides the minimum electrical resistancewhen the magnetization direction of the free layer 10 matches that ofthe second ferromagnetic layer 8 in the pinned layer 12.

Accordingly, the spin-valve film l's electrical resistance varies withan applied external magnetic field. It is possible to detect an externalmagnetic field by reading this resistance change.

As will be clearly understood from the above description, the spin-valvefilm 1 contains the pinned layer 12 having the layered ferrimagneticstructure. The pinned layer 12 includes the surface oxidation layer 7formed by oxidizing the surface of the non-magnetic intermediate layer6. This formation easily generates spin-dependent scattering. Further,it is possible to thin the non-magnetic layer 9 between the pinned layer12 and the free layer 10. Owing to these features, the spin-valve film 1improves a magnetoresistive-effect change and provides good sensitivityagainst an external magnetic field.

The following describes a second embodiment of themagnetoresistive-effect thin film according to the present inventionwith reference to FIG. 3. A spin-valve film 21 is of a so-calledtop-type and is characterized by a layered ferrimagnetic structurehaving a surface oxidation layer on a free layer.

The spin-valve film 21 comprises a base layer 23, a first ferromagneticlayer 24, a non-magnetic intermediate layer 25, a surface oxidationlayer 26, a second ferromagnetic layer 27, a third ferromagnetic layer28, a non-magnetic layer 29, a fourth ferromagnetic layer 30, a secondnon-magnetic layer 31, a fifth ferromagnetic layer 32, anantiferromagnetic layer 33, and a protective layer 34 which are layeredsuccessively on a substrate 22. It should be noted that the firstferromagnetic layer 24, the non-magnetic intermediate layer 25, thesurface oxidation layer 26, the second ferromagnetic layer 27, and thethird ferromagnetic layer 28 compose a free layer 35 having a layeredferrimagnetic structure. The fourth ferromagnetic layer 30, the secondnon-magnetic layer 31, and the fifth ferromagnetic layer 32 compose apinned layer 36 having a layered ferrimagnetic structure.

The substrate 22, the base layer 23, the antiferromagnetic layer 33, andthe protective layer 34 for the spin-valve film 21 have almost the sameconfigurations as those of the substrate 2, the base layer 3, theantiferromagnetic layer 4, and the protective layer 11 for thespin-valve film 1 described in the first embodiment. Accordingly,detailed description about these components is omitted here.

The first ferromagnetic layer 24, the second ferromagnetic layer 27, andthe third ferromagnetic layer 28 are formed of magnetic materialsshowing good soft magnetic characteristics such as an Ni—Fe alloy, Co,and an alloy containing one of Co, Ni, and Fe. Together with thenon-magnetic intermediate layer 25 and the surface oxidation layer 26 tobe described later, the first ferromagnetic layer 24, the secondferromagnetic layer 27, and the third ferromagnetic layer 28 form thefree layer 35 having the so-called layered ferrimagnetic structure.

The free layer 35's magnetization direction varies with an externalmagnetic field: Using the layered ferrimagnetic structure for the freelayer 35 can decrease an apparent magnetic moment for the free layer 35without thinning it. This makes it possible to improve the spin-valvefilm 21's reproduction sensitivity.

The non-magnetic intermediate layer 25 and the surface oxidation layer26 function as non-magnetic layers formed in the middle of theabove-mentioned layered ferrimagnetic structure. The surface oxidationlayer 26 is formed by oxidizing the surface of the non-magneticintermediate layer 25. It is desirable to form the non-magneticintermediate layer 25 of Ru with the thickness of 0.4 to 1.2 nm.

Since the surface oxidation layer 26 is formed by oxidizing the surfaceof the non-magnetic intermediate layer 25, the surface oxidation layer26 and the non-magnetic intermediate layer 25 almost maintain the sameinterface. The spin-valve film 21 is formed unbrokenly. Forming thesurface oxidation layer 26 containing Ru—O smoothes the interface. Thiscan cause the so-called mirror reflection which enables reflection andscattering by maintaining spin directions of electrons. The mirrorreflection of electrons dramatically improves the probability ofelectron's spin-dependent scattering. Consequently, it is possible toimprove a magnetoresistive-effect change for the spin-valve film 21.

The surface oxidation layer 26 is formed in the free layer 35 having thelayered ferrimagnetic structure. This makes it possible to extremelythin the non-magnetic layer 29 between the pinned layer 36 and the freelayer 35 compared to the prior art. It is further possible to improve amagnetoresistive-effect change for the spin-valve film 21.

While the surface oxidation layer 26 is formed by oxidizing the surfaceof the non-magnetic intermediate layer 25, the thickness of the surfaceoxidation layer 26 generally should be 0.4 nm or less.

Several methods are available for forming the surface oxidation layer 26by oxidizing the surface of the non-magnetic intermediate layer 25. Forexample, one method exposes the non-magnetic intermediate layer 25 to anoxygen atmosphere having a pressure lower than the atmospheric pressure.There is also provided the plasma oxidization method including ECR(electron cyclotron resonance) and the ICP (inductively coupled plasma).

The non-magnetic layer 29 is formed of a conductive non-magneticmaterial such as, say, Cu, Cu—Ni alloy, or the like. Forming thenon-magnetic layer 29 between the pinned layer 36 and the free layer 35provides the giant magneto-resistivity on the spin-valve film 21. Asmentioned above, the non-magnetic layer 29 can be thinner than thenon-magnetic layer between the pinned layer and the free layer on theconventional spin-valve film. More specifically, it is desirable to setthe non-magnetic layer 29's thickness to approximately 2 run.

The pinned layer 36 is exchange-coupled to the antiferromagnetic layer33 to fix the magnetization direction. The pinned layer 36 comprises thefourth ferromagnetic layer 30, the second non-magnetic layer 31, and thefifth ferromagnetic layer 32 to form the layered ferrimagneticstructure. Like the first ferromagnetic layer 24, the secondferromagnetic layer 27, and the third ferromagnetic layer 28, the fourthferromagnetic layer 30 and the fifth ferromagnetic layer 32 are formedof magnetic materials showing good soft magnetic characteristics. Thesecond non-magnetic layer 31 is a non-magnetic layer formed in themiddle of the layered ferrimagnetic structure and is capable of usingRu, Rh, Ir, Re, and the like.

Providing the pinned layer 36 with the layered ferrimagnetic structuredecreases a magnetic moment on the pinned layer 36 and also decreasesdemagnetization applied to the free layer 35.

In this spin-valve film 21, the pinned layer 36 is provided in contactwith the antiferromagnetic layer 33. Consequently, the pinned layer 36is magnetized in a given direction due to an exchange coupling forcegenerated between the pinned layer 36 and the antiferromagnetic layer33. Since the non-magnetic layer 29 is formed between the free layer 35and the pinned layer 36, the free layer 35's magnetization directioneasily rotates in response to a slight external magnetic field.

When an external magnetic field is applied to the thus configuredspin-valve film 21, a magnetization direction of the free layer 35 isdetermined according to this external magnetic field's direction andintensity. The spin-valve film 21 provides the maximum electricalresistance when the magnetization direction of the free layer 35 differsfrom that of the pinned layer 36 by 180°. The spin-valve film 21provides the minimum electrical resistance when the magnetizationdirection of the free layer 35 matches that of the pinned layer 36.

Accordingly, the spin-valve film 21's electrical resistance varies withan applied external magnetic field. It is possible to detect an externalmagnetic field by reading this resistance change.

As will be clearly understood from the above description, the spin-valvefilm 21 contains the free layer 35 having the layered ferrimagneticstructure. The free layer 35 includes the surface oxidation layer 26formed by oxidizing the surface of the non-magnetic intermediate layer25. This formation easily generates spin-dependent scattering. Further,it is possible to thin the nonmagnetic layer 29 between the pinned layer36 and the free layer 35. Owing to these features, the spin-valve film21 improves a magnetoresistive-effect change and provides goodsensitivity against an external magnetic field.

The above description relates to the spin-valve film 21 which uses thepinned layer 36 having the layered ferrimagnetic structure. It is to bedistinctly understood that the present invention is not limited theretobut may be applicable to the pinned layer 36 having a single layer.

The above-mentioned magnetoresistive-effect thin film is applicable to amagnetoresistive-effect element. The magnetoresistive-effect elementaccording to the present invention comprises a magnetoresistive-effectthin film having a high magnetoresistive-effect change. As will bedescribed later, there is provided an MR head as an example of thedevice using the magnetoresistive-effect element.

The following describes an MR head according to the present invention.The following description applies to a case where the MR head accordingto the present invention is applied to a composite magnetic head 40. Itshould be noted that the composite magnetic head 40 is used for harddisks.

As shown in FIG. 4, the composite magnetic head 40 comprises an MR headand an inductive magnetic head. The inductive magnetic head is layeredon the MR head. The MR head is provided as a reproduction head. Theinductive magnetic head is provided as a recording head.

First, the MR head is described.

In the MR head, a first magnetic shield layer 43 is formed on asubstrate 41 through the intermediary of an insulation layer 42. On thisfirst magnetic shield layer 43, the above-mentioned spin-valve film 1 isformed through the intermediary of the insulation layer 42. There areformed bias layers 44 a and 44 b in a longer direction of the spin-valvefilm 1. There are formed connection terminals 45 a and 45 b in contactwith the bias layers 44 a and 44 b. A second magnetic shield layer 46 isformed on the bias layers 44 a and 44 b and the connection terminals 45a and 45 b through the intermediary of the insulation layer 42.

The substrate 41 comprises a highly hard non-magnetic material. Thehighly hard non-magnetic material includes, say, alumina-titaniumcarbide (AlTiC). The substrate 4 l's edge forms an ABS (Air BearingSurface) facing a disk-shaped storage medium.

The insulation layer 42 is formed of an insulation material. Theinsulation material includes, say, Al₂O₃, SiO₄, and the like. Thecomposite magnetic head 40 is fabricated with layers. The insulationlayer 42 actually comprises a plurality of layers. However, anillustration thereof is omitted here.

The first magnetic shield layer 43 and the second magnetic shield layer46 function so that the spin-valve film 1 rejects magnetic fields notfor reproduction out of signal magnetic fields from a magnetic storagemedium. Namely, a magnetic field not for reproduction is led to thefirst magnetic shield layer 43 and the second magnetic shield layer 46.Only a signal magnetic field for reproduction is led to the spin-valvefilm 1. This aims at improving high-frequency characteristics and readresolution of the spin-valve film 1. As will be described later, thesecond magnetic shield layer 46 also functions as a lower-layer core.

The first magnetic shield layer 43 and the second magnetic shield layer46 are formed of a soft magnetic material. The soft magnetic materialincludes, say, Sendust (Fe—Al—Si alloy), FeTa, and Co-based amorphousmaterial. The first magnetic shield layer 43 and the second magneticshield layer 46 may have the layered structure comprising two or moremagnetic thin-film layers by alternately layering a soft magneticthin-film layer and a non-magnetic thin-film layer both made from aCo-based amorphous material.

The spin-valve film 1 is a magnetic sensor which senses a signalmagnetic field from the magnetic storage medium. As mentioned above, thespin-valve film 1 comprises the base layer 3, the antiferromagneticlayer 4, the first ferromagnetic layer 5, the non-magnetic intermediatelayer 6, the surface oxidation layer 7, the second ferromagnetic layer8, the non-magnetic layer 9, the free layer 10 and the protective layer11 which are successively layered. In FIG. 4, however, an illustrationof each layer is omitted.

As mentioned above, the surface oxidation layer 7 is formed by oxidizingthe non-magnetic intermediate layer 6's surface. Further, it isdesirable to form the non-magnetic intermediate layer 6 of Ru. Moreover,the surface oxidation layer 7 is formed of Ru—O because it is formed byoxidizing the non-magnetic intermediate layer 6's surface.

Thus, the pinned layer 12 having the layered ferrimagnetic structureincludes the surface oxidation layer formed by oxidizing thenon-magnetic intermediate layer 6's surface. Because of this, thespin-valve film 1 increases probability of a spin-dependent scatteringoccurrence and improves a magnetoresistive-effect change. It is possibleto thin the non-magnetic layer 9 between the pinned layer 12 and thefree layer 10, further improving a magnetoresistive-effect change. Sincethe MR head 20 comprises the spin-valve film 1 with a highmagnetoresistive-effect change, this head improves sensitivity againstmagnetic fields from an information storage medium and providesexcellent reproduction outputs.

While the surface oxidation layer 7 is formed by oxidizing the surfaceof the non-magnetic intermediate layer 6, the thickness of the surfaceoxidation layer 7 generally should be 0.4 nm or less.

A pair of bias layers 44 a and 44 b provides a function for applying abias magnetic field to the spin-valve film 1 and forcing a single domainto a magnetic domain of each ferromagnetic layer in the spin-valve film1. This function also supplies a sense current to the spin-valve film 1.The bias layers 44 a and 44 b each are electrically and magneticallyconnected to both ends of the spin-valve film 1.

The bias layers 44 a and 44 b are formed of a hard magnetic material atboth ends of the spin-valve film 1 in a longer direction. This hardmagnetic material includes, say, CoNiPt, CoCrPt, and the like. It may bepreferable to form an electrode layer on the bias layers 44 a and 44 b.

The connection terminals 45 a and 45 b provide the bias layers 44 a and44 b with a sense current. The connection terminals 45 a and 45 b areformed in a thin film made from a conductive and low-resistance metalmaterial. Preferable materials for the connection terminals 45 a and 45b are, say, Cr, Ta, Ti, W, Mo, Cu, and the like.

The following describes the inductive magnetic head.

The inductive magnetic head comprises the thin-film coil 47 which isembedded in the insulation layer 42 and is formed on the second magneticshield layer 46. The insulation layer 42 is formed around the thin-filmcoil 47. The upper-layer core 48 is formed on the insulation layer 42 inwhich the thin-film coil 47 is embedded. The second magnetic shieldlayer 46 and the upper-layer core 48 form the magnetic core 49.

The thin-film coil 47 records information onto a magnetic storage mediumaccording to a change in a recording current supplied from an externalconnection terminal (not shown). The thin-film coil 47 is formed so thatit is wound around the magnetic core 49. Both ends of the thin-film coil47 are exposed externally. The above-mentioned external connectionterminals are formed at these ends. The thin-film coil 47 is formed of aconductive material such as copper.

The upper-layer core 48 and the second magnetic shield layer 46 form aclosed magnetic circuit and function as the magnetic core 49 for theinductive magnetic head. At the front end, the upper-layer core 48 andthe second magnetic shield layer 46 are exposed to the ABS and areseparated to foin a specified gap g. At the rear end, the upper-layercore 48 and the second magnetic shield layer 46 are formed so that theycontact with each other. The gap g is used for a recording gap of theinductive magnetic head. The upper-layer core 48 is formed of a softmagnetic material such as NiFe and the like.

As will be clearly understood from the above description, theabove-mentioned MR head indicates a high probability of causingspin-dependent scattering. Accordingly, this MR head is formed of thespin-valve film 1 having a large magnetoresistive-effect change. Becauseof this, the MR head provides good sensitivity against a magnetic fieldfrom an information storage medium, produces a high output duringinformation reproduction, and is thus appropriate for high-densityrecording.

The above description explains the case where the MR head uses theso-called bottom-type spin-valve film 1 described as the firstembodiment. The present invention is not limited thereto. For example,the MR head can also use the so-called top-type spin-valve film 21described as the second embodiment.

The above description exemplifies the MR head as a device which uses themagnetoresistive-effect element. The magnetoresistive-effect elementaccording to the present invention can be applied to devices other thanthe MR head. Specifically, the magnetoresistive-effect element accordingto the present invention is also applicable to magnetic sensors and thelike such as a geomagnetic direction sensor.

As will be clearly understood from the above description, thebottom-type spin-valve film 1 contains the pinned layer 12 having thelayered ferrimagnetic structure. The pinned layer 12 includes thesurface oxidation layer 7 formed by oxidizing the surface of thenon-magnetic intermediate layer 6. This formation easily generatesspin-dependent scattering. Further, it is possible to thin thenon-magnetic layer 9 between the free layer 10 and the pinned layer 12.Owing to these features, the spin-valve film 1 improves amagnetoresistive-effect change aid provides good sensitivity against anexternal magnetic field.

As will be clearly understood from the above description, the spin-valvefilm 21 contains the free layer 35 having the layered ferrimagneticstructure. The free layer 35 includes the surface oxidation layer 26formed by oxidizing the surface of the non-magnetic intermediate layer25. This formation easily generates spin-dependent scattering. Further,it is possible to thin the non-magnetic layer 29 between the free layer35 and the pinned layer 36. Owing to these features, the spin-valve film21 improves a magnetoresistive-effect change and provides goodsensitivity against an external magnetic field.

The MR head according to the present invention is formed of theso-called bottom-type spin-valve film 1 or the so-called top-typespin-valve film 21. Because of this, the MR head provides goodsensitivity against a magnetic field from an information storage mediumand produces a high output during information reproduction. Accordingly,the MR head according to the present invention is appropriate forhigh-density recording.

EXAMPLES

The following describes specific embodiments according to the presentinvention based on experiment results.

First, The following describes improvement of a resistance variation anda magnetoresistive-effect change in the bottom-type spin-valve filmaccording to the above-mentioned first embodiment based on the firstembodiment and a comparative example 1.

Example 1

First, sputtering or the like is used to successively form a Ta layer,an NiFe layer, and a PtMn layer on a glass substrate. Layer thicknessesare set to 5 nm for the Ta layer, 2 nm for the NiFe layer, and 20 nm forthe PtMn layer.

Then, sputtering or the like is used to successively form a CoFe layerand an Ru layer on the PtMn layer. Layer thicknesses are set to 1.1 nmfor the CoFe layer and 0.8 nm for the Ru layer.

The Ru layer's surface is oxidized to form an Ru—O layer by exposingthis surface to an oxygen atmosphere having a pressure lower than theatmospheric pressure.

Then, sputtering or the like is used to successively form a CoFe layer,a Cu layer, and a CoFe layer on the Ru—O layer for creating a spin-valvefilm. Layer thicknesses are set to 2.2 run for the CoFe layer and 3.2 mfor the Cu layer formed on the Ru—O layer. A layer thickness is set to2.5 run for the CoFe layer formed on the Cu layer. Thereafter, heattreatment is applied to the PtMn layer at 265° C. for 4 hours toregulate this layer.

Comparative Example 1

A spin-valve film is fabricated in the same manner as for the firstexample except that the Ru layer surface is not oxidized. Namely, thespin-valve film for the comparative example 1 does not have a surfaceoxidation layer made from Ru—O.

Resistance variations are measured and magnetoresistive-effect changesare computed when a magnetic field is applied to the spin-valve filmsfabricated for the first example and the comparative example 1.

When evaluating spin-valve film characteristics, an MR ratio anddR/square are used as evaluation parameters. The MR ratio is amagnetoresistive-effect change in the spin-valve film. The dR/squaredenotes a resistance variation per unit area on the spin-valve film.

FIG. 5 shows dR/square and the MR ratio when a magnetic field is appliedto the first example. FIG. 6 shows dR/square and the MR ratio when amagnetic field is applied to the comparative example 1.

As shown in FIGS. 5 and 6, it has been found that the spin-valve filmhaving the Ru—O layer for the first example causes more resistancevariation than the comparative example 1. Further, it has been foundthat the spin-valve film having the Ru—O layer for the first examplecauses more magnetoresistive-effect change than the comparativeexample 1. Specifically, the spin-valve film having the Ru—O layer forthe first example shows values as large as 11.31% of the MR ratio and1.54 Ω of the dR/square.

According to these measurements, it has been found that themagnetoresistive-effect change can be improved by using the layeredferrimagnetic structure for pinned layers of the bottom-type spin-valvefilm and forming a surface oxidation layer of Ru—O in the layeredferrimagnetic structure.

Then, with respect to the second example, the following describes athickness of the Ru—O layer formed in accordance with an Ru layerthickness, and also relationship between the Ru layer thickness and acoercive force for the entire thin film.

Example 2

First, a Cu layer, a CoFe layer, and an Ru layer are successively formedon a glass substrate to form a thin film. A plurality of thin films isfabricated by changing thicknesses of the Ru layer. Each thin film isexposed to the atmospheric air to oxidize the Ru layer. A coercive forceis measured for each thin film.

FIG. 7 shows a result of the second example. According to this result,it has been found that the coercive force for the entire thin filmdrastically increases by setting the Ru layer thickness to 0.4 nm orless. It has been suggested that setting the Ru layer thickness to 0.4nm or less progresses oxidation not only to the Ru layer, but also tothe underlying CoFe layer. Meanwhile, it has been found that the entirethin film maintains a relatively low coercive force when the Ru layerthickness exceeds 0.4 nm. It has been suggested that thickening the Rulayer over 0.4 nm prevents oxidization to the underlying CoFe layer andoxidizes the Ru layer halfway.

Accordingly, it has been found that the Ru layer is oxidized just to thedepth of 0.4 run from the surface when it is exposed in an oxygenatmosphere with a pressure below the atmospheric pressure. In otherwords, it has been clear that the thickness of the Ru—O layer formed byoxidizing the Ru layer surface should be 0.4 run or less.

Then, the following describes improvement of a resistance variation anda magnetoresistive-effect change in the top-type spin-valve filmaccording to the above-mentioned second embodiment based on a thirdexample and a comparative example 2. Also described are effects ofthinning the Cu layer between the pinned layer and the free layer on aresistance variation and a magnetoresistive-effect change based on afourth example and a comparative example 3.

Example 3

First, sputtering or the like is used to successively form a Ta layer,an NiFe layer, and an Ru layer on a glass substrate. Layer thicknessesare set to 5 mm for the Ta layer, 2 nm for the NiFe layer, and 0.8 nmfor the Ru layer.

The Ru layer's surface is oxidized to form an Ru—O layer by exposingthis surface to an oxygen atmosphere having a pressure lower than theatmospheric pressure.

Then, sputtering or the like is used to successively form an NiFe layer,a CoFe layer, a Cu layer, a CoFe layer, an Ru layer, a CoFe layer, aPtMn layer, and a Ta layer on the Ru—O layer for creating a spin-valvefilm. Layer thicknesses are set to 1 nm for the NiFe layer formed on theRu—O layer, 2 nm for the CoFe layer formed on the NiFe layer, 3.2 nm forthe Cu layer, 2.2 nm for the CoFe layer formed on the Cu layer, 0.8 nmfor the Ru layer, formed on the CoFe layer, 1.1 nm for the CoFe layerformed on the Ru layer, 20 nm for the PtMn layer, and 5 nm for the Talayer formed on the PtMn layer. Thereafter, heat treatment is applied tothe PtMn layer at 265° C. for ˜4 hours to regulate this layer.

Comparative Example 2

A spin-valve film is fabricated in the same manner as for the secondexample except that the Ru layer surface is not oxidized.

Example 4

A spin-valve film is fabricated in the same manner as for the thirdexample except that a layer thickness is set to 2.2 nm for the Cu layerbetween the pinned layer and the free layer.

Comparative Example 3

A spin-valve film is fabricated in the same manner as for thecomparative example 2 except that a layer thickness is set to 2.2 nm forthe Cu layer between the pinned layer and the free layer.

Resistance variations are measured and magnetoresistive-effect changesare computed when a magnetic field is applied to the spin-valve filmsfabricated for the third example, the comparative example 2, the fourthexample, and the comparative example 3.

FIG. 8 shows dR/square and the MR ratio when a magnetic field is appliedto the third example. FIG. 9 shows dR/square and the MR ratio when amagnetic field is applied to the comparative example 2. FIG. 10 showsdR/square and the MR ratio when a magnetic field is applied to thefourth example FIG. 11 shows dR/square and the MR ratio when a magneticfield is applied to the comparative example 3.

As shown in FIGS. 8 and 9, it has been found that the spin-valve filmhaving the Ru—O layer for the third example causes more resistancevariation than the comparative example 2 without the Ru—O layer.Further, it has been found that the spin-valve film having the Ru—Olayer for the third example causes more magnetoresistive-effect changethan the comparative example 2 without the Ru—O layer.

Moreover, as shown in FIG. 10, it has been found that the fourth exampleusing the thin Cu layer with a thickness of 2.2 nm drastically improvesa resistance variation and a magnetoresistive-effect change compared tothe third example using the Cu layer with a thickness of 3.2 run.Meanwhile, as shown in FIG. 11, the comparative example 3 without theRu—O layer uses the thin Cu layer with a thickness of 2.2 nm. Thecomparative example 3 shows very slight improvement in themagnetoresistive-effect change compared to the comparative example 2using the Cu layer with a thickness of 3.2 run without the Ru—O layer.Specifically, the fourth example using the Cu layer with a thickness of2.2 nm indicates the MR ratio of 10.6% and the dR/square of 1.85 Ω. Thethird example using the Cu layer with a thickness of 3.2 nm indicatesthe MR ratio of 8.90% and the dR/square of 1.26 Ω.

According to this experiment, it has been found that themagnetoresistive-effect change can be improved by using the layeredferrimagnetic structure for the free layer in the top-type spin-valuefilm and forming the surface oxidation layer of Ru—O in this layeredferrimagnetic structure. Further, it has been found that themagnetoresistive-effect change remarkably improves by thinning thenon-magnetic layer between the pinned layer and the free layer.

1-15. (canceled)
 16. A magnetoresistive-effect element comprising: a substrate formed of a nonmagnetic nonconductive material; a base layer formed of a nonmagnetic conductive material on said substrate; a free layer formed on said base layer, said free layer comprising: a first ferromagnetic layer; a non-magnetic intermediate layer formed on said first ferromagnetic layer; a surface oxidation layer formed on a surface of said non-magnetic intermediate layer; a second ferromagnetic layer formed on said surface oxidation layer; and a third ferromagnetic layer formed on said second ferromagnetic layer; a non-magnetic layer formed on said free layer; a pinned layer formed on said non-magnetic layer; said pinned layer comprising: a fourth ferromagnetic layer; a second non-magnetic intermediate layer; a fifth ferromagnetic layer formed on said second non-magnetic intermediate layer; and an antiferromagnetic layer formed on said pinned layer.
 17. The magnetoresistive-effect thin film according to claim 16, wherein said non-magnetic intermediate layer is formed of Ru.
 18. The magnetoresistive-effect element according to claim 16, wherein said surface oxidation layer has a thickness of no more than 0.4 nm.
 19. A magnetoresistive-effect magnetic head comprising: a pair of zonal magnetic shield members, a magnetoresistive-effect thin film formed between said pair of magnetic shield members, a pair of bias layers formed at both ends of said magnetoresistive-effect thin film along a longer direction, and a pair of thin-film lead electrodes each formed just on said bias layer on a substrate, wherein said magnetoresistive-effect thin film comprises: a substrate formed of a nonmagnetic nonconductive material; a base layer formed of a nonmagnetic conductive material on said substrate; a free layer formed on said base layer, said free layer comprising: a first ferromagnetic layer; a non-magnetic intermediate layer formed on said first ferromagnetic layer; a surface oxidation layer formed on a surface of said non-magnetic intermediate layer; a second ferromagnetic layer formed on said surface oxidation layer; and a third ferromagnetic layer formed on said second ferromagnetic layer; a non-magnetic layer formed on said free layer; a pinned layer formed on said non-magnetic layer; said pinned layer comprising: a fourth ferromagnetic layer; a second non-magnetic intermediate layer; a fifth ferromagnetic layer formed on said second non-magnetic intermediate layer; and an antiferromagnetic layer formed on said pinned layer.
 20. The magnetoresistive-effect magnetic head according to claim 19, wherein said non-magnetic intermediate layer is formed of Ru.
 21. The magnetoresistive-effect magnetic head according to claim 19, wherein said surface oxidation layer has a thickness of no more than 0.4 mm. 